Last year, I started playing in the very occasional Boot Hill game of Regina, she of the web-serialized, historical novel Five Dollar Mail. Gina's group likes to go somewhat rules-lite. Gina gave me a page of information on the setting, basically boiling down to "a small town with a pony express stop in the Nebraska Territory of the early 1860s" and "magic exists, but it's not flashy, more historic-feeling." And she said: "come up with the character you want to play."
After a bit of consideration, this is what I sent her:
From The Western Gunfighter Encyclopedia (Wheeler, 1975):
CROWE, GIDEON (1820-?) - gunman, spiritualist, and carnival performer. Born into a once prominent Baltimore family, Crowe was the son of a former minister and a fortune-teller and sometime-actress, described as "of Gipsie [sic] blood" and purported to be the illegitimate daughter of infamous occultist/confidence artist Alessandro di Cagliostro (Giuseppe Balsamo). Crowe allegedly fought in the service of the British East India Company in the latter days of the campaign against the Thuggee cult. Returning to North American, he was obscurely involved with the East Texas Regulator-Moderator War. He joined John Joel Glanton and his scalphunters, but deserted them shortly before the band fled Chihuahua as outlaws. He performed sharpshooting shows, and European-style phantasmagoria--"ghost shows," utilizing a primitive antecedent of the slide projector, for several years in theaters and dance-halls in San Francisco's Barbary Coast. His ultimate fate is unrecorded.
Despite being little known today, Crowe was the the inspiration for a dime novel serial, "The Sideshow of Prof. Crowe" in Mundsen & Grandee's Old West Library (1880). Here the carnival aspects are played up, and Crowe has accomplices in the form of "the mighty Negro, Samson," a mute strong-man; and "the sultry Gypsie, Appollonia," a medium. In addition to being a "dead shot with a pistol, " Crowe was said to be "master of the esoteric sciences" and "adept in the secrets of the Hindoo." In the pulp era, he served as the inspiration for a series of short stories by T. Mallory beginning in 1934 with "Satan's Gunman" in Western Mystery. Here, his associates were much the same, but Crowe himself is gifted with more of a supernatural nature. He is a skilled medium and occultist, and referred to as "the Frontier Faust." It is intimated that he is under some contract to send evil-doers to hell and is--at least once--called "the Devil's Pinkerton" by an adversary. The pulp stories, in turn, served to inspire Italian horror filmmaker Lucio Balsamo to pounce on the "Spaghetti Western" craze with Pistolero del Diavolo (1967, U.S. title: Satan's Gun). Gideon Crowe was portrayed by an actor credited (likely pseudonymously) as "Max Shreck," who is practically a Lee Van Cleef lookalike--which makes him not a bad likeness of the real Crowe given the one daguerreotype extant, believed to date from the mid-1850s.
My purpose here--writing it as "fictional non-fiction"--was to suggest hooks and interesting tidbits that might be of interest to the GM without necessarily assuming what was "true" in her world. Historically removed and masked by legend, who's to say what the truth of Gideon Crowe--the character who would result--was?
It's the sort of thing I would be able to get behind as a GM, but I was unsure how Gina would take it.
Luckily, she took it completely in the spirit intended. A few days later she emailed me the character with game abilities, fleshed out with tidbits inspired by the write-up.
I don't suggest something like this would work for ever campaign, or every player-GM team, but I think the collaborative nature of game worldbuilding should start from the very beginning, not just when the adventure begins.